It used to be accessible at http://tinderbox.dev.gentoo.org. It contained tarballs of all the binary packages in the stable branch (output of continuous automated build testing, I believe). Useful in emergencies, such as when you butcher something on your system needed for emerge to work.

Now there's nothing at that URL._________________History teaches us that men and nations behave wisely once they have exhausted all other alternatives. -- Abba Eban